Pattern formation method using levenson-type mask and method of manufacturing levenson-type mask

ABSTRACT

A method of forming a pattern including a first pattern portion having a first minimum dimension and a second pattern portion having a second minimum dimension includes a first exposure step of performing exposure using a Levenson-type mask and a second exposure step of performing exposure using a half tone-type mask. When second minimum dimension is 1.3 time or more than the first minimum dimension, the exposure amount of the second exposure step is set to be equal to or smaller than the exposure amount of the first exposure step.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No.11/637,698, filed on Dec. 13, 2006, now U.S. Pat. No. 7,682,760 claimingpriority of Japanese Patent Application No. 2005-361831, filed on Dec.15, 2005, the entire contents of each of which are hereby incorporatedby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a pattern formation method and a methodof manufacturing a Levenson-type mask.

2. Description of the Background Art

In semiconductor devices such as semiconductor integrated circuits, aphotolithography technique may be used to form electrodes orinterconnections. In a photolithography step, an exposure step isperformed to expose a resist in a prescribed shape through a photomask.The resist is formed, for example, of a photosensitive resin and formedinto a prescribed shape by performing development after the exposurestep.

The mask used in the exposure step has a light transmitting portion anda light shielding portion. The photomask includes a phase shift mask forchanging a phase of light transmitted through the light transmittingportion to increase a resolution. The phase shift mask includes aLevenson-type mask and a half tone-type mask. These photomasks use theinterference action of light to increase a resolution.

In the Levenson-type mask, when a resist, which is for example positive,arranged on a surface of a substrate is processed into a prescribedshape, a light transmitting portion is formed on one side of oppositesides of a part to allow light to pass through and a light transmittingportion is formed on the other side to cause phase reversal with respectto the phase of light of the light transmitting portion on one side. TheLevenson-type mask is a photomask formed such that the phases of lighton opposite sides of a part are reverse to each other thereby improvingthe resolution at the part.

In the half tone-type mask, when a resist arranged on a surface of asubstrate is processed into a prescribed shape, a light transmittingportion is formed in one of a part or a surrounding part of the part anda light-shielding portion is formed in the other, which allows light topartially pass through it and additionally reverses the phase, therebyimproving the resolution at the above-noted part.

Japanese Patent Laying-Open No. 2002-229181 discloses a Levenson-typemask for forming a light shielding portion for isolated pattern elementformation and a plurality of light shielding portions for formingperiodic pattern elements on a transparent substrate. This Levenson-typemask has a phase shift portion and a light transmission portion arrangedon opposite sides of the light shielding portion for isolated patternelement formation. A phase shift portion and a light transmittingportion are arranged on opposite sides of the light shielding portionfor forming periodic pattern elements. The remaining part of thetransparent substrate is covered with a light shielding portion. It isdisclosed that the width of the phase shift portion for isolated patternelement formation is made approximately equal to the width of the phaseshift portion for forming periodic pattern elements.

Japanese Patent Laying-Open No. 2003-168640 discloses a method ofmanufacturing a semiconductor device in which the phases of a fine linepattern formed by a phase shift mask and of a shifter pattern adjacentthereto in a certain range are reverse to each other. Preferably, atleast four shifter patterns are provided with a fine line pattern formedby a phase edge interposed at the middle, and the adjacent shifterpatterns are arranged to have opposite phases.

In photolithography, a method of performing exposures multiple times isknown to form a fine part on a surface of a substrate.

For example, Japanese Patent Laying-Open No. 11-283904 discloses anexposure method including: a high-resolution exposure in which a patternof a part difficult in line-width control is transferred using a phaseshift pattern; and a normal exposure in which a pattern of a part easierin line-width control is transferred to a photoresist layer withoutusing a phase shift pattern while the part of the photoresist layer towhich the pattern has already been transferred by the high-resolutionexposure is protected by a light-shielding portion of the mask pattern.

Furthermore, U.S. Pat. No. 5,858,580 discloses use of two maskprocesses. The first mask is a phase shift mask and the second mask is asingle phase structure mask. The single phase structure mask allowsexposure in such a manner that the region of the phase shift is noterased. In the single phase structure mask, an exposure is performed soas to avoid formation at the undesired part in a region other than thepart formed by the phase shift mask.

In addition, Japanese Patent Laying-Open No. 01-283925 discloses anexposure method of patterning densely in a first region and patterningmore coarsely than the first region in a second region. The first regionis exposed by a mask pattern having a phase shift pattern to cause phasereversal of exposure light and the second region is exposed by a maskpattern having a light transmitting region and a non-transmittingregion.

Japanese Patent Laying-Open No. 2004-247606 discloses a method ofmanufacturing a semiconductor device, in which in forming a gatecomprised of a gate electrode and a gate interconnection, only a gateelectrode pattern is formed by a double exposure process using a binarymask or a half tone mask as a first mask and a Levenson-type mask as asecond mask, and thereafter a gate interconnection pattern is formed byan exposure process using a binary mask or a half tone mask as a thirdmask.

As described above, a phase shift mask or multiple exposure allowsformation of a pattern including a part having a small minimumdimension. However, for example in a semiconductor device, furtherminiaturization is likely to be sought, and forming a fine pattern withhigh dimensional accuracy is currently desired.

In a Levenson-type mask, a light-shielding film such as a chrome film isarranged on a surface of a transparent substrate. An opening portion isformed to transmit light. The opening portion mainly includes a samephase opening portion and a reverse phase opening portion. The samephase opening portion is a region through which light is transmittedwithout a phase change and is formed of a main surface of thetransparent substrate. In the reverse phase opening portion, a concaveportion is formed or a shifter is arranged in the transparent substrate.The light passing through the reverse phase opening portion has itsphase reversed.

Some Levenson-type masks including a concave portion in a transparentsubstrate as a reverse phase opening portion have an undercut portionformed such that the concave portion extends to below the end portion ofa light-shielding film. In this Levenson-type mask, when the reversephase opening portions are adjacent to each other, the undercut portionsare adjacent to each other. With increased miniaturization ofsemiconductor devices, the distance between the undercut portions isreduced. As a result, the contact area between the light-shielding filmarranged on the surface of the transparent substrate and the transparentsubstrate is reduced, so that the light-shielding film may sometimesstrip away.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a pattern formationmethod to allow formation of a fine pattern. Another object of thepresent invention is to provide a method of manufacturing aLevenson-type mask to allow formation of a fine pattern.

In accordance with an aspect of the present invention, a method offorming a pattern including a first pattern having a first minimumdimension and a second pattern having a second minimum dimensionincludes: a first exposure step of performing an exposure using aLevenson-type mask; and a second exposure step of performing an exposureusing a half tone-type mask. When the second minimum dimension is atleast 1.3 times the first minimum dimension, an exposure amount of thesecond exposure step is set to be at most an exposure amount of thefirst exposure step.

In accordance with another aspect of the present invention, a method offorming a pattern including a first pattern having a first minimumdimension and a second pattern having a second minimum dimensionincludes: a first exposure step of performing an exposure using aLevenson-type mask; and a second exposure step of performing an exposureusing a half tone-type mask. When the second minimum dimension is atleast 1.0 time and at most 1.1 times the first minimum dimension, anexposure amount of the second exposure step is set to be greater than anexposure amount of the first exposure step.

In accordance with an aspect of the present invention, a method ofmanufacturing a Levenson-type mask is provided. The Levenson-type maskincludes a transparent substrate and a light shielding film arranged ona main surface of the transparent substrate and having a plurality ofopening portions. The opening portion includes a same phase openingportion and a reverse phase opening portion. The reverse phase openingportion has a concave portion formed in the main surface. The concaveportion has an undercut portion formed to extend to below an end portionof the reverse phase opening portion. The same phase opening portionsand the reverse phase opening portions are set in pairs to form a firstpattern in a processed object. The method includes an opening portionsetting step of defining the same phase opening portion and the reversephase opening portion on opposite sides of the first pattern. Theopening portion setting step includes a step of setting the same phaseopening portion in at least one of the opening portions that form pairsopposed to each other, in order of increasing distance between thepairs.

In accordance with another aspect of the present invention, a method ofmanufacturing a Levenson-type mask is used in manufacturing asemiconductor device having a first pattern formed in an active regionof an element region and a second pattern formed in an element isolationregion. The method includes an opening portion setting step of setting asame phase opening portion and a reverse phase opening portion as anopening portion on opposite sides of the first pattern. When the secondpattern is arranged between regions exposed through the opening portionsand a distance between the region exposed through the opening portionand the second pattern is at most such a distance that has a substantialeffect on dimensional variations of the second pattern, the openingportion setting step includes a step of setting the same phase openingportion and the reverse phase opening portion on opposite sides of thesecond pattern, and an expansion step of expanding the same phaseopening portion and the reverse phase opening portion to allow formationof the second pattern.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of a resist pattern formed in a firstembodiment.

FIG. 2 is a schematic plan view of a Levenson-type mask in the firstembodiment.

FIG. 3 is a schematic cross sectional view of the Levenson-type mask inthe first embodiment.

FIG. 4 is a schematic plan view of a half tone-type mask in the firstembodiment.

FIG. 5 is a graph illustrating the amount of exposure in the firstembodiment.

FIG. 6 is a graph illustrating ILS value in the first embodiment.

FIG. 7 is a schematic plan view where the exposure amount ratio of thehalf tone-type mask in the first embodiment is reduced.

FIG. 8 is a schematic perspective view where a resist test is conductedin the first embodiment.

FIG. 9 is a graph showing the result of the resist test in the firstembodiment.

FIG. 10 is a graph of the amount of exposure illustrating the result ofa first test in a second embodiment.

FIG. 11 is a graph of ILS value illustrating the result of the firsttest in the second embodiment.

FIG. 12 is a graph of the amount of exposure illustrating the result ofa second test in the second embodiment.

FIG. 13 is a graph of ILS value illustrating the result of the secondtest in the second embodiment.

FIG. 14 is a graph of the amount of exposure illustrating the result ofa third test in the second embodiment.

FIG. 15 is a graph of ILS value illustrating the result of the thirdtest in the second embodiment.

FIG. 16 is a schematic plan view of a resist pattern formed in a thirdembodiment.

FIG. 17 is a schematic plan view of a Levenson-type mask in the thirdembodiment.

FIG. 18 is a schematic plan view of a half tone-type mask in the thirdembodiment.

FIG. 19 is a graph of the amount of exposure illustrating the result ofa first test in the third embodiment.

FIG. 20 is a graph of the amount of exposure illustrating the result ofa second test in the third embodiment.

FIG. 21 is a schematic plan view of a resist pattern formed in a fourthembodiment.

FIG. 22 is a schematic plan view of a Levenson-type mask in the fourthembodiment.

FIG. 23 is a schematic cross sectional view of the Levenson-type mask inthe fourth embodiment.

FIG. 24 is a schematic plan view of a Levenson-type mask in acomparative example in the fourth embodiment.

FIG. 25 is a schematic cross sectional view of the Levenson-type mask inthe comparative example in the fourth embodiment.

FIG. 26 is an illustration of a method of setting a same phase openingpotion and a reverse phase opening portion in a region of openingportions of the Levenson-type mask in the fourth embodiment.

FIG. 27 is a schematic plan view of a resist pattern formed in a fifthembodiment.

FIG. 28 is a schematic plan view of a Levenson-type mask in the fifthembodiment.

FIG. 29 is a schematic plan view of a half tone-type mask in the fifthembodiment.

FIG. 30 is a first step illustration where a same phase opening portionand reverse phase opening portion are set in a region of openingportions of the Levenson-type mask in the fifth embodiment.

FIG. 31 is a second step illustration where a same phase opening portionand reverse phase opening portion are set in a region of openingportions of the Levenson-type mask in the fifth embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

Referring to FIG. 1 to FIG. 9, a pattern formation method in a firstembodiment of the present invention will be described. In the presentembodiment, a method of manufacturing a semiconductor device will bedescribed by way of example. In the present embodiment, of phase shiftmasks, a Levenson-type mask and a half tone-type mask are used. Usingthe phase shift masks, exposures are performed multiple times.

FIG. 1 shows a schematic plan view of a pattern arranged on a surface ofa processed object in the present embodiment. In the present embodiment,a resist pattern 10 is formed on a surface of a substrate 9 as aprocessed object. Substrate 9 in the present embodiment has a conductivefilm such as a polysilicon film arranged on a surface of a siliconwafer. In addition, an organic antireflection coating is deposited at athickness of 80 nm on the surface of the polysilicon film. In thepresent embodiment, a resist formed on this organic antireflectioncoating is patterned. A resist pattern 10 is a photoresist formed at thesurface of substrate 9. In the present embodiment, a positive resist isused.

Resist pattern 10 includes a first pattern portion 10 a and a secondpattern portion 10 b. First pattern portion 10 a is, for example, aportion that is a gate electrode of a field effect transistor. Secondpattern portion 10 b is, for example, a portion that is aninterconnection portion for connecting the gate electrode. First patternportion 10 a is a pattern of a fine line or a part requiring dimensionalaccuracy. Second pattern portion 10 b is a pattern having dimensionslarger than first pattern portion 10 a or requiring less dimensionalaccuracy than first pattern portion 10 a.

In the present invention, the minimum dimension refers to the dimensionof the distance (span) across a pattern, among the dimensions of atarget pattern. First pattern portion 10 a has a first minimum dimensionD_(min1). The first minimum dimension in the present embodiment is awidth perpendicular to the direction in which first pattern portion 10 aextends. Second pattern portion 10 b has a second minimum dimensionD_(min2). The second minimum dimension in the present embodiment is awidth of first pattern portion 10 a. In the present embodiment, thefirst minimum dimension is formed to be smaller than the second minimumdimension.

A photolithography step is performed to form a photoresist having such ashape. In the photolithography step, for example, a resist film of aphotosensitive resin arranged evenly on the surface of a conductive filmserving as a processed film on a substrate is exposed and then developedso that the resist is left at a part of a desired shape. Furthermore,using the left resist as a mask, the processed film is etched therebypatterning the processed film in a desired shape.

In the present embodiment, an exposure for forming first pattern portion10 a is performed with a Levenson-type mask. An exposure for formingsecond pattern portion 10 b is performed with a half tone-type mask.

FIG. 2 shows a schematic plan view of a Levenson-type mask in thepresent embodiment. FIG. 3 shows a cross sectional view taken along lineIII-III as viewed from the arrow in FIG. 2.

The Levenson-type mask includes, for example, a transparent substrate 19formed of silica glass or the like. A light shielding film 1 is arrangedon a surface of transparent substrate 19 to block light. Light shieldingfilm 1 is formed, for example, of a Cr film.

Light shielding film 1 has an opening portion as a light transmittingregion to allow passage of light. In the present embodiment, the openingportion has a same phase opening portion 1 a and a reverse phase openingportion 1 b. Same phase opening portion 1 a and reverse phase openingportion 1 b are arranged on opposite sides of a part corresponding tofirst pattern portion 10 a (see FIG. 1).

In same phase opening portion 1 a, the surface of transparent substrate19 is formed in a flat shape. The same phase region of the lighttransmitting region of the Levenson-type mask is formed of the mainsurface of transparent substrate 19. In reverse phase opening portion 1b, a concave portion 24 is formed at a surface of transparent substrate19. The reverse phase region of the light transmitting region of theLevenson-type mask is formed of concave portion 24 formed at a surfaceof transparent substrate 19. Concave portion 24 is formed such that thephase of light passing through reverse phase opening portion 1 b isreversed. For example, concave portion 24 is formed such that the lightpassing through reverse phase opening portion 1 b has its phase shiftedby 180° as compared with the light passing through same phase openingportion 1 a.

Concave portion 24 in the present embodiment has an undercut portion 24a formed to improve dimensional accuracy. Undercut portion 24 a isformed to extend to the inner side of the end portion in reverse phaseopening portion 1 b of light shielding film 1. In other words, lightshielding film 1 has a portion serving as eaves at reverse phase openingportion 1 b.

Although the Levenson-type mask in the present embodiment has a concaveportion formed in a transparent substrate to reverse the phase of light,the present invention is not limited to such a manner. For example, ashifter for reversing the phase may be arranged at the reverse phaseopening portion at the surface of the transparent substrate.

FIG. 4 shows a schematic plan view of a half tone-type mask in thepresent embodiment. The half tone-type mask has a light shieldingportion 5 b at the surface of transparent substrate 19. Light shieldingportion 5 a is formed to completely block light. Light shielding portion5 a is formed, for example, of a Cr film. Light shielding portion 5 a isformed such that the portion subjected to exposure using theLevenson-type mask is not subjected to exposure. Light shielding portion5 a is formed corresponding to the opening portion of the Levenson-typemask. A half tone portion 5 b is arranged at the surface of transparentsubstrate 19 to form second pattern portion 10 b (see FIG. 1) of resistpattern 10. Half tone portion 5 b is formed corresponding to the shapeof second pattern portion 10 b of the resist pattern.

Half tone portion 5 b in the present embodiment is formed to allow thelight of exposure to be partially transmitted. Half tone portion 5 b isformed such that the transmitted light has its phase reversed. Half toneportion 5 b in the present embodiment includes a phase shifter arrangedat the surface of transparent substrate 19. The half tone portion is notlimited to the arrangement of a phase shifter and may be formed to allowa part of exposure light to be transmitted with its phase reversed.

Referring to FIG. 1, in the present embodiment, an exposure is performedso that the first minimum dimension D_(min1) of first pattern portion 10a is smaller than the second minimum dimension D_(min2) of secondpattern portion 10 b. In the present embodiment, resist pattern 10 isformed such that the second minimum dimension D_(min2) is 1.3 times orgreater than the first minimum dimension D_(min1). Resist pattern 10 isformed such that the first minimum dimension D_(min1) of first patternportion 10 a is 70 nm.

First, an acrylic-based positive resist is applied as a photosensitiveresin at a film thickness of 180 nm on the surface of an organicantireflection coating. A pre-exposure heating treatment is performed onthis resist film.

Next, a first exposure step is performed to form first pattern portion10 a. The first exposure step is exposure using the Levenson-type mask.In the first exposure step, the Levenson-type mask having same phaseopening portion 1 a and reverse phase opening portion 1 b (see FIG. 2)is used.

In the first exposure step in the present embodiment, ArF excimer laser(wavelength of 193 nm) is used to perform an exposure on the resistfilm. The widths of same phase opening portion 1 a and reverse phaseopening portion 1 b of light shielding film 1 of the Levenson-type maskin the present embodiment (see FIG. 2) are 140 nm each. The distancebetween same phase opening portion 1 a and reverse phase opening portion1 b is 140 nm. Exposure is performed with this Levenson-type mask underthe conditions of NA of 0.82 and Conv. (σ=0.40). Here, NA is numericalaperture. Conv. is a circular aperture stop of conventionalillumination. Moreover, σ is a ratio between illumination optical NA andprojection lens system NA as viewed from the substrate (wafer).

Then, a second exposure step is performed to form second pattern portion10 b. The second exposure step is exposure using the half tone-typemask. In the second exposure step, exposure is performed using the halftone-type mask having light shielding portion 5 a and half tone portion5 b (see FIG. 4).

In the second exposure step, the part of light shielding portion 5 a inFIG. 4 blocks light. In other words, in the second exposure step, anexposure is performed such that the range subjected to the exposure inthe first exposure step is not subjected to exposure again. In half toneportion 5 b shown in FIG. 4, light is partially transmitted with itsphase reversed.

In the present embodiment, a mask having a half tone portion having atransmittance of 6% is used. In the second exposure step, exposure wasperformed under the conditions of NA of 0.80 and Conv. (σ=0.85). Theamount of exposure to the resist in the second exposure step is not morethan the amount of exposure to the resist in the first exposure step. Inother words, the exposure steps are performed in such a manner that theamount of exposure performed on the irradiated object such as a resistusing the half tone-type mask is not more than the amount of exposureperformed using the Levenson-type mask.

After the first exposure step and the second exposure step, the resistfilm was developed thereby forming a pattern as shown in FIG. 1.Although the first exposure step is followed by the second exposure stepin the present embodiment, the second exposure step may be performedfirst. In other words, the exposure using the half tone-type mask may beperformed first.

In the first exposure step, the light passing through same phase openingportion 1 a has its phase unchanged for exposure. The light passingthrough reverse phase opening portion 1 b has its phase reversed. At thepart of first pattern portion 10 a, interference of light takes place.This can prevent the part of first pattern portion 10 a from beingexposed and improve the dimensional accuracy in first pattern portion 10a. In other words, a fine first pattern portion 10 a can be formed.

The present embodiment employs multiple exposure in which, of resistpattern 10, first pattern portion 10 a is subjected to exposure usingthe Levenson-type mask and second pattern portion 10 b is subjected toexposure using the halftone-type mask. In the multiple exposure, alatent image of the part first subjected to exposure may be influencedby fog of light in performing an exposure later.

For example, in the present embodiment, referring to FIG. 1, a latentimage of first pattern portion 10 a of resist pattern 10 is influencedwhen an exposure is performed later using the half tone-type mask. Forexample, if the amount of exposure in the second exposure step ofperforming an exposure using the half tone-type mask is too much, thedimensional accuracy of first pattern portion 10 a may be deteriorated.

FIG. 5 shows a graph of the result of an exposure test in the presentembodiment. FIG. 5 is a graph of a composite optical image in firstpattern portion 10 a (see FIG. 1) of the resist pattern in the presentembodiment. The axis of abscissas shows the distance from the center inthe width direction of first pattern portion 10 a to the outer side ofthe width direction. The location of 0 is the center in the widthdirection of the first pattern portion. The axis of ordinates shows thelight intensity in the Levenson-type mask and the half tone-type mask.

In the exposure test, exposures were performed with various ratiosbetween the exposure amounts of the Levenson-type mask and the halftone-type mask. The test was also conducted for exposure using only theLevenson-type mask.

Referring to FIG. 5, as the ratio of the exposure amount of theLevenson-type mask is smaller, the slope of the composite optical imagebecomes smaller, which suggests that the latent image is degraded. Inother words, with the lower ratio of the exposure amount of theLevenson-type mask, the exposure of the half tone-type mask has greatereffect and the dimensional accuracy is deteriorated.

For example, in the range where the distance from the center of thefirst pattern portion is greater than about 0.03 μm (in the range wherethe line width of the first pattern portion of the resist pattern isgreater than 0.06 μm), in order to obtain a composite optical image withapproximately the same slope as using only the Levenson-type mask, theexposure amount of the Levenson-type mask has to be at least 0.8 time ormore than the exposure amount of the half tone-type mask. In addition,when the exposure amount of the Levenson-type mask is 1.0 time or morethan the exposure amount of the half tone-type mask, the latent imagehaving the dimensional accuracy equivalent to or higher than only usingthe Levenson-type mask can be obtained more reliably.

Here, ILS (Image Log Slope) value is employed as a basis to define theexposure amount ratio. ILS value shows the slope of logarithm of theimage intensity and defined such that ILS value=(1/Is)×(ΔI/Δx). Here, Isis a slice value and (ΔI/Δx) shows the gradient of the light intensityat the point of the slice value of the light intensity line.

In the present embodiment, a line width of 0.08 μm is used as a typicalvalue for calculating a slice value. In a device with a design rule(design standard) of 65 nm, the line width of an electrode,interconnection or the like is about 60 nm or more and 70 nm or less.Based on that here the line width of the resist film is about 80 nm, atypical value of a line width is defined for calculating a slice value.In other words, this line width is a generic line width in asemiconductor device with a design rule of 65 nm. In this line width,the range from the center of the line width to the positions −0.04 μm ormore and +0.04 μm or less therefrom is employed for slice values.

FIG. 6 shows a graph illustrating ILS values where the exposure amountratio between the Levenson-type mask and the half tone-type mask isvaried. The axis of abscissas shows the exposure amount ratio and theaxis of ordinates shows the ILS value. As the exposure amount ratio ofthe Levenson-type mask is increased, the ILS value is increased. Asdescribed above, as can be seen from the graph in FIG. 5, if theexposure amount ratio between the Levenson-type mask and the halftone-type mask is 1:1, an excellent composite latent image can beobtained. In FIG. 6, the ILS value where the exposure amount ratio is1:1 is about 0.8 time the ILS value only with the Levenson-type mask andis approximately 34. In other words, the ILS value of approximately 34ensures the adequate slope of the exposure mount of the compositeoptical image, resulting in a first pattern portion with highdimensional accuracy. In other words, a minute first pattern portion canbe formed.

As described above, the exposure amount of the Levenson-type mask ispreferably 1.0 time or more than the exposure amount of the halftone-type mask. However, as the exposure amount ratio of the halftone-type mask is reduced, the dimensions of the light shielding portionof the half tone-type mask is reduced. As a result, the light shieldingportion may be reduced in size below the mask manufacturing limit. Withthe size below the mask manufacturing limit, it becomes impossible tomanufacture a mask. Considering manufacturing a mask, the exposureamount of the Levenson-type mask is more preferably 1.0 time or more and1.2 times or less than the exposure amount of the half tone-type mask.

It is advantageous to set the exposure amount using the Levenson-typemask greater than the exposure amount using the half tone-type mask whenthe minimum dimension of the second pattern portion formed with the halftone-type mask is 1.3 times or greater than the minimum dimension of thefirst pattern portion formed with the Levenson-type mask. In theexposure step, the focus tolerance of an exposure apparatus may become aproblem. More specifically, the dimensional variations in which thefocusing of the exposure apparatus is varied may not fall within apermissible range. The problem of focus tolerance is conspicuous whenthe second minimum dimension is less than 1.3 times the first minimumdimension. If the second minimum dimension is 1.3 times or greater thanthe first minimum dimension, the exposure amount of the Levenson-typemask is set greater than the exposure amount of the half tone-type maskin order to form a first pattern portion with high dimensional accuracy.In other words, a minute first pattern portion can be formed. Moreover,advantageously, a line width can be shrunken in a method ofmanufacturing a semiconductor device with a design rule of 65 nm orless.

In the present embodiment, the exposure is performed in such a mannerthat the exposure amount of the Levenson-type mask is equal to orgreater than the exposure amount of the half tone-type mask.Accordingly, the contrast of latent image at the part of theLevenson-type mask can be improved so that a minute semiconductor devicecan be provided. In other words, a semiconductor device with improveddimensional accuracy can be provided.

In order to reduce the exposure amount of the half tone-type mask, theintensity of light from a light source may be weakened, or the exposuretime may be shortened. Besides, Optical Proximity Correction (OPC) maybe employed.

FIG. 7 shows a schematic plan view of a half tone-type mask employingOptical Proximity Correction. In the half tone portion formed at thesurface of transparent substrate 19, half tone portion 5 b is reduced insize to form a half tone portion 5 c. In this way, bias is set to reducethe size of the half tone portion, so that the amount of exposure forthe irradiated object can be reduced. As a guide of a mask bias amountof the half tone portion, for example, in an isolated pattern with thedistance between half tone portions of 2000 nm or more and the minimumwidth dimension of 70 nm as a basic pattern, the mask bias is set at 5nm or more and 10 nm or less on either side.

The kind of resists used in the exposure step also influences theoptical latent image. Now, the kinds of resists to be used will bedescribed.

FIG. 8 shows a schematic perspective view of a basic patternillustrating the dependency of Optical Proximity Effect (OPE) on aresist. In the basic pattern, an exposure is performed on a resist 27through a half tone-type mask 26. Half tone-type mask 26 has a half toneportion 26 a.

Half tone portion 26 a is formed in a linear shape. Half tone portions26 a are formed such that they extend parallel to each other. Anexposure region 27 a of resist 27 becomes linear. In such a basicpattern, the distance between half tone portions 26 a is a space size S.The width of half tone portion 26 a is W. The width of exposure region27 a is CD (Critical Dimension) value. In the present embodiment, ascanner-type exposure apparatus is used where the CD value isapproximately one-quarter of width W of half tone portion 26 a.

FIG. 9 shows a graph illustrating the characteristic of CD values in twokinds of resists. In the present embodiment, an acrylic-based positiveresist is used as a resist film. The axis of abscissas shows space sizeS and the axis of ordinates shows CD value. In the part where space sizeS is smaller, each of the CD values rises sharply.

Here, (the maximum value of CD value—the minimum value of CD value) inresist A is greater than (the maximum value of CD value—the minimumvalue of CD value) in resist B. In other words, resist A has OpticalProximity Effect greater than resist B. In this way, the OPEcharacteristic varies depending on the kind of resists. Therefore, aresist excellent in the OPE characteristic is preferably selected. Forexample, in the case of a resist with a large value of (the maximumvalue of CD value—the minimum value of CD value), when a pattern havinga small pitch is formed, it largely deviates from the expected value.Therefore, when Optical Proximity Correction is performed, a patternhaving a small pitch may attain the size below the mask manufacturinglimit. In FIG. 9, it is preferable to use resist B rather than resist A.

By selecting a resist excellent in the OPE characteristic as a resist,the range of choice of the exposure amount ratio can be broadened andthe exposure amount ratio can be changed without changing the expectedvalue of the manufactured pattern.

Second Embodiment

Referring to FIG. 10 to FIG. 15, a pattern formation method in a secondembodiment of the present invention will be described. The presentembodiment is similar to the first embodiment in that it includes afirst exposure step of performing an exposure using a Levenson-type maskand a second exposure step of performing an exposure using a halftone-type mask. In addition, similar to the first embodiment, when thesecond minimum dimension of the second pattern is 1.3 times or greaterthan the first minimum dimension of the first pattern, the exposureamount of the second exposure step is set equal to or smaller than theexposure amount of the first exposure step. In the present embodiment,in the second exposure step, an exposure is performed using a halftone-type mask having a half tone portion with reduced transmittance. Inthe present embodiment, a test was conducted in a manner similar to thetest method in the first embodiment.

FIG. 10 shows a first graph illustrating the result of a first test inthe present embodiment. FIG. 1 shows a second graph illustrating theresult of the first test in the present embodiment. In the first test,the exposure amount of the first exposure step performed using aLevenson-type mask and the exposure amount of the second exposure stepperformed using a half tone-type mask were set at a ratio of 1:1. Theexposure amount was found at each of the parts where the transmittanceof the half tone portion of the half tone-type mask was varied from 6%to 0%.

FIG. 10 shows a graph of a composite optical image of a first pattern ofthe resist pattern formed by the Levenson-type mask (see FIG. 1). Theaxis of abscissas shows a distance from the center in the widthdirection of the linear part formed by the Levenson-type mask, and theaxis of ordinates shows the light intensity. With the reducedtransmittance of the half tone-type mask, the light intensity at theposition 0 μm approaches 0.

FIG. 11 shows a graph of ILS value in the first test. The axis ofabscissas shows the transmittance of the half tone portion of the halftone-type mask, and the axis of ordinates shows the ILS value. The maskhaving the transmittance of 0% at the half tone portion of the halftone-type mask serves as a normal mask blocking light which does nothave a half tone portion.

As shown in FIG. 11, as the transmittance of the half tone portion isreduced, the ILS value tends to be larger. It can be understood that thedimensional accuracy of the first pattern portion improves with thereduced transmittance of the half tone portion. Referring to FIG. 11,where the ratio between the exposure amount of the Levenson-type maskand the exposure amount of the half tone-type mask is 1:1, the ILS valuecan be approximately 34 or more with the transmittance of 6% or less ofthe half tone-type mask.

FIG. 12 shows a first graph illustrating the result of a second test inthe present embodiment. FIG. 13 shows a second graph illustrating theresult of the second test in the present embodiment. In the second test,the exposure amount of the Levenson-type mask is set relatively smallerthan the first test. In the second test, the ratio between the exposureamount of the Levenson-type mask and the exposure amount of the halftone-type mask was set at 0.8:1.

FIG. 12 shows a composite optical image of the part of the first patternof the resist pattern formed by the Levenson-type mask. FIG. 13 shows agraph of ILS value in the second test. Referring to FIG. 12, as thetransmittance of the half tone-type mask is reduced, the light intensityat position 0 μm approaches 0. Referring to FIG. 13, when the ratiobetween the exposure amount of the Levenson-type mask and the exposureamount of the half tone-type mask is 0.8:1, the ILS value can beapproximately 34 or more with the transmittance of 4% or less of thehalf tone-type mask.

FIG. 14 shows a first graph illustrating the result of a third test inthe present embodiment. FIG. 15 shows a second graph illustrating theresult of the third test in the present embodiment. In the third test,the exposure amount of the Levenson-type mask is further reducedrelatively to the second test. In the third test, the ratio between theexposure amount of the Levenson-type mask and the exposure amount of thehalf tone-type mask was set at 0.6:1.

FIG. 14 shows a graph of the composite optical image of the part of thefirst pattern of the resist pattern formed by the Levenson-type mask.FIG. 15 shows a graph of ILS value in the third test. Referring to FIG.14, the light intensity at the position 0 μm approaches 0 by reducingthe transmittance of the half tone portion of the half tone-type mask.Referring to FIG. 15, when the ratio between the exposure amount of theLevenson-type mask and the exposure amount of the half tone-type mask is0.6:1, the ILS value can be approximately 34 or more with thetransmittance of 4% or less of the half tone-type mask.

In this manner, even if the ratio between the exposure amount of theLevenson-type mask and the exposure amount of the half tone-type mask isvaried, the transmittance of the half tone portion of the half tone-typemask is adjusted correspondingly, so that the dimensional accuracy of apattern formed by the Levenson-type mask can be improved.

The other configuration, action, effect, and method are similar to thoseof the first embodiment and therefore the description will not berepeated here.

Third Embodiment

Referring to FIG. 16 to FIG. 20, a pattern formation method in a thirdembodiment of the present invention will be described. The patternformation method in the present embodiment is similar to the firstembodiment in that it includes a first exposure step of performing anexposure using a Levenson-type mask and a second exposure step ofperforming an exposure using a half tone-type mask. In the presentembodiment, when the second minimum dimension of the second pattern is1.0 time or greater and 1.1 times or smaller than the first minimumdimension of the first pattern, the exposure amount of the secondexposure step is set to be greater than the exposure amount of the firstexposure step.

FIG. 16 is a schematic plan view of a resist pattern in the thirdembodiment. Resist patterns 11-13 are formed at a surface of substrate9. Resist pattern 13 is arranged at a position where it is sandwichedbetween resist pattern 11 and resist pattern 12. Resist pattern 13 isformed by the half tone-type mask.

Resist pattern 11 includes a first pattern portion 11 a and a secondpattern portion 11 b. Resist pattern 12 includes a first pattern portion12 a and a second pattern portion 12 b. First pattern portions 11 a, 12a are formed by the Levenson-type mask. Second resist patterns 11 b, 12b are formed by the half tone-type mask.

First pattern portion 11 a, 12 a serves, for example, as a gateelectrode of a field effect transistor. An active region 50 is a regionformed by implanting an impurity in a surface of substrate 9 to serve,for example, as a source region or a drain region of a field effecttransistor. The part of resist pattern 13 has, for example, aninterconnection formed therein.

In the present embodiment, attention will be paid to resist pattern 13sandwiched between the resist patterns formed by the Levenson-type mask.The interconnection pattern at the surface of substrate 9 which isformed by resist pattern 13 has a width of 70 nm at the linear part (thewidth of the part corresponding to width L1 of resist pattern 13 in FIG.16).

FIG. 17 shows a schematic plan view of the Levenson-type mask in thepresent embodiment. The Levenson-type mask includes a light shieldingfilm 2. Light shielding film 2 has same phase opening portions 2 a, 2 cand reverse phase opening portions 2 b, 2 d. Same phase opening portion2 a and reverse phase opening portion 2 b are paired so that firstpattern portion 11 a of resist pattern 11 is formed as a line patternbetween same phase opening portion 2 a and reverse phase opening portion2 b. Similarly, same phase opening portion 2 c and reverse phase openingportion 2 d are paired so that first pattern portion 12 a of resistpattern 12 is formed (see FIG. 16).

FIG. 18 shows a schematic plan view of the half tone-type mask in thepresent embodiment. The half tone-type mask includes transparentsubstrate 19. Light shielding portions 6 a, 6 c are formed on a surfaceof transparent substrate 19. Light shielding portions 6 a, 6 c areformed to allow light to slightly pass through. Half tone portions 6 b,6 d, 6 e are formed on a surface of transparent substrate 19. Lightshielding portions 6 a, 6 c are formed corresponding to the openingportions of the Levenson-type mask. Half tone portions 6 b, 6 d areformed corresponding to second pattern portions 11 b, 12 b of resistpatterns 11, 12, respectively. Half tone portion 6 e is formedcorresponding to resist pattern 13 (see FIG. 16). In this way, thelinear portion of resist pattern 13 subjected to exposure using the halftone-type mask is sandwiched between first pattern portions 11 a, 12 aof resist patterns 11, 12 subjected to exposure using the Levenson-typemask.

When exposures are performed using these Levenson-type mask and halftone-type mask at the ratio of exposure amount of 1:1, for example, thelight shielding portion width of the interconnection pattern arrangedbetween the opening portions of the Levenson-type mask and formed by thehalf tone-type mask is 90 nm, which corresponds to length L1 in thewidth direction of resist pattern 13 (see FIG. 16).

FIG. 19 shows a graph of a composite optical image where the exposureamount ratio between the Levenson-type mask and the half tone-type maskis 1:1. The axis of abscissas shows a position in cross section takenalong line A-A in FIG. 16. The axis of ordinates shows the lightintensity of the composite optical image. In FIG. 19, the part Acorresponds to the part of resist pattern 13 in FIG. 16. The minimumvalue Imin of the light intensity is 0.123.

Now, the exposure where the exposure amount ratio between theLevenson-type mask and the half tone-type mask is 0.6:1 will bedescribed. In other words, the exposure amount of the Levenson-type maskis relatively reduced. In this case, the light shielding portion widthof the interconnection pattern arranged between the opening portions ofthe Levenson-type mask and formed by the half tone-type mask is 110 nm,which corresponds to the length L1 in the width direction of resistpattern 13 (see FIG. 16).

FIG. 20 shows a graph of a composite optical image where the exposureamount ratio between the Levenson-type mask and the half tone-type maskis 0.6:1. The part A corresponds to the part of resist pattern 13 inFIG. 16. A small value can be achieved as the minimum value Imin of thelight intensity is 0.063.

Referring to FIG. 19 and FIG. 20, when the ratio of the exposure amountof the Levenson-type mask to the exposure amount of the half tone-typemask is increased, the minimum value Imin of the light intensity of thepattern formed by the half tone-type mask may not be reduced enough. Thefirst exposure step using the Levenson-type mask has an effect on alatent image to be formed by the halftone-type mask, so that the minimumvalue Imin of the light intensity of the line pattern to be formed bythe half tone-type mask is increased.

As a result, for example, a defect such as a disconnection may takeplace at the part formed by the half tone-type mask. More specifically,in the exposure process in the first exposure step, the exposure amountand focus are set as the optimum conditions, and this focus (focusing)may sometimes vary under some influence given by the apparatus so thatexposure may be performed in the varied state. Here, the latent imageformed by the phase shift-type mask influences the latent image formedby the half tone-type mask, which may cause a defect in the patternformed by the half tone-type mask.

This defect appears conspicuously in the step of forming a first patternhaving a first minimum dimension and forming a second pattern having asecond minimum dimension where the second minimum dimension is 1.1 timesor less than the first minimum dimension. In this case, the exposureamount of the second exposure step with the half tone-type mask is setto be greater than the exposure amount of the first exposure step withthe Levenson-type mask. This method can suppress a defect in thatpattern of the second patterns formed by the half tone-type mask whichis adjacent to the first pattern formed by the Levenson-type mask.Specifically, a defect of the second pattern sandwiched between thefirst patterns can be suppressed.

For example, in FIG. 16, a disconnection at the linear part of resistpattern 13 sandwiched between first pattern portions 11 a, 12 a ofresist patterns 11, 12 can be suppressed.

In the present embodiment, the contrast of a latent image formed by thehalf tone-type mask can be improved, and a defect of a pattern formed bythe half tone-type mask can be suppressed. In other words, in the secondexposure step using the half tone-type mask, the focus tolerance inexposure can be improved.

Now, the manner of use of the pattern formation method described in thepresent embodiment and the pattern formation methods described in thefirst and second embodiments will be described.

A semiconductor device A and a semiconductor device B are formed whichare designed with a minimum gate length of 70 nm of the gate lengths offield effect transistors. The gate electrode of the field effecttransistor is formed by the Levenson-type mask and the interconnectionportion is formed by the half tone-type mask.

Here, as for semiconductor device A, the minimum dimension of theinterconnection portion is set at 100 nm. The interconnection portion ofsemiconductor device A is arranged such that the process margin informing a latent image in exposure is larger. The dimensional accuracyrequired of the gate length of semiconductor device A is under strictconditions. On the other hand, as for semiconductor device B, theminimum dimension of the interconnection portion is set at 70 nm, whichis equal to the minimum dimension of the gate length. Theinterconnection portion of semiconductor device B has a small processmargin of forming a latent image in exposure. However, the dimensiondescribed above may vary ±10% or so in the finishing state due tovariations in manufacturing processes.

In such a case, as for semiconductor device A, as shown in the firstembodiment, the exposure amount with the half tone-type mask is set tobe equal to or be smaller than the exposure amount with theLevenson-type mask, resulting in a gate electrode having highdimensional accuracy within the range of the process margin of forming alatent image of an interconnection portion.

As for semiconductor device B, as shown in the present embodiment, theexposure amount with the half tone-type mask is set to be greater thanthe exposure amount with the Levenson-type mask, thereby ensuring aprocess margin of forming a latent image in forming an interconnectionportion.

The other configuration, action, effect, and method are similar to thoseof the first and second embodiments and therefore the description willnot be repeated here.

Fourth Embodiment

Referring to FIG. 21 to FIG. 26, a method of manufacturing aLevenson-type mask in a fourth embodiment of the present invention willbe described.

FIG. 21 shows a schematic plan view of a resist pattern formed in thepresent embodiment. In the present embodiment, a Levenson-type mask anda half tone-type mask are used. Resist patterns 11-13 are formed on asurface of substrate 9 with a conductive film (not shown) such aspolysilicon interposed therebetween. Resist pattern 11 includes firstpattern portion 11 a and second pattern portion 11 b. Resist pattern 12includes first pattern portion 12 a and second pattern portion 12 b.

First pattern portions 11 a, 12 a are formed using the Levenson-typemask. Furthermore, using first pattern portions 11 a, 12 a as a mask,the conductive film is patterned, resulting in, for example, the gateelectrode of a field effect transistor. Active region 50 serves as asource region or a drain region of a field effect transistor. Secondpattern portions 11 b, 12 b are formed using the half tone-type mask.Resist pattern 13 is formed using the half tone-type mask. Resistpattern 13 forms, for example, an interconnection.

In the present embodiment, the distance corresponding to distance L2between first pattern portion 11 a and the linear portion of resistpattern 13 is 160 nm. For example, the distance between the gateelectrode of a field effect transistor and an interconnection is 160 nm.In the present embodiment, the distance between first pattern portion 12a and the linear portion of resist pattern 13 is equal to the distancebetween first pattern portion 11 a and the linear portion of resistpattern 13.

In the present embodiment, the width of a line formed corresponding towidth L3 of first pattern portion 11 a, 12 a is 60 nm. The width of aline formed corresponding to the width of the linear portion of resistpattern 13 is equal to the width corresponding to width L3. For example,the width of the gate electrode of a field effect transistor is 60 nm.

FIG. 22 shows a schematic plan view of the Levenson-type mask in thepresent embodiment. FIG. 23 shows a cross sectional view taken alongline XXIII-XXIII as viewed from the arrow in FIG. 22.

The Levenson-type mask in the present embodiment includes a lightshielding film 3 on a transparent substrate 21. Light shielding film 3is formed to block light. Light shielding film 3 has same phase openingportions 3 a, 3 c and reverse phase opening portions 3 b, 3 d. In thepresent embodiment, same phase opening portions 3 a, 3 c are formedadjacent to each other.

Referring to FIG. 23, light shielding film 3 is formed on the surface oftransparent substrate 21. The main surface of transparent substrate 21is located in same phase opening portions 3 a, 3 c. A concave portion 22is formed at each of reverse phase opening portions 3 b, 3 d in thesurface of transparent substrate 21. Concave portion 22 is formed suchthat the phase of light passing through reverse phase opening portions 3b, 3 d is shifted by half-wavelength. In other words, it is formed suchthat the phase is reversed. Concave portion 22 has an undercut portion22 a.

In the Levenson-type mask, a same phase opening portion and a reversephase opening portion have to be arranged on opposite sides of a patternsuch as a line pattern to be formed. In other words, a pattern to beformed has to be sandwiched between a same phase opening portion and areverse phase opening portion.

In the step of manufacturing a Levenson-type mask, an opening portionhas to be set for a pattern to be formed. The method of manufacturing aLevenson-type mask includes an opening portion setting step of setting asame phase opening portion and a reverse phase opening portion. One samephase opening portion and one reverse phase opening portion are set inpair, so that one pattern is formed in the subsequent exposure. Aconcave portion is formed in the surface of the substrate correspondingto the set reverse phase opening portion. The present embodimentincludes a step of setting a same phase opening portion in at least oneof the opening portions that form pairs opposed to each other, of thepairs of same phase opening portions and reverse phase opening portions,in the order of increasing distance between the pairs.

Referring to FIG. 22, opening portions are formed on opposite sides ofthe part corresponding to each of resist pattern 11 and resist pattern12. Here, with reference to distance L4 between the opening portionsthat form pairs opposed to each other, it is assumed that the distancebetween the pairs is shorter than the other portions. In this case, asame phase opening portion is set in at least one of them. In thepresent embodiment, same phase opening portions 3 a, 3 c are formed inboth of the opening portions that form pairs opposed to each other.

The configuration of the half tone-type mask in the present embodimentis similar to that of the half tone-type mask in the third embodiment(see FIG. 18).

FIG. 24 shows a schematic plan view of a Levenson-type mask as acomparative example in the present embodiment. FIG. 25 shows a crosssectional view taken along line XXV-XXV as viewed from the arrow in FIG.24.

Referring to FIG. 24, the Levenson-type mask as a comparative example isdifferent in a method of setting a same phase opening portion and areverse phase opening portion in the opening portions. Same phaseopening portion 3 a and reverse phase opening portion 3 b are paired. Inaddition, same phase opening portion 3 c and reverse phase openingportion 3 d are paired. In the Levenson-type mask as a comparativeexample, the opening portions that form two pairs opposed to each otherare set as reversal opening portions 3 b, 3 d. The opening portionscorresponding to the opposite sides of resist pattern 13 are set asreverse phase opening portions 3 b, 3 d.

Referring to FIG. 25, the main surface of transparent substrate 21 isformed in same phase opening portions 3 a, 3 c. A concave portion 23 isformed at each of reverse phase opening portions 3 b, 3 d in the mainsurface of transparent substrate 21. Concave portion 23 has an undercutportion 23 a.

In the step of manufacturing a Levenson-type mask, for example, a lightshielding film having an opening portion is formed on the surface of atransparent substrate. Then, dry etching is performed to form a portionwhich is concave from the main surface of the transparent substrate.Then, wet etching is additionally performed to form an undercut portionbelow the opening portion of the light shielding film.

For example, in the comparative example, undercut portion 23 a of 100 nmis formed farther from the edge of each of reverse phase openingportions 3 b, 3 d. The distance between reverse phase opening portion 3b and reverse phase opening portion 3 d is 400 nm. In this case, thecontact width L5 between light shielding film 3 and transparentsubstrate 21 is 200 nm. In this way, when the ratio between contactwidth L5 and the distance between reverse phase opening portion 3 b andreverse phase opening portion 3 d is ½ or less, the undercut portionsopposed to each other reduce the contact area between light shieldingfilm 3 and transparent substrate 21, which may cause the light shieldingfilm to be partially stripped off. Specifically, when the distancebetween opening portions is reduced with further miniaturization of linepatterns, the inconvenience of partial stripping of the light shieldingfilm is remarkable.

In the opening portion setting step of setting an opening portion, asame phase opening portion is set in at least one of the openingportions that form pairs opposed to each other, in the order ofincreasing distance between the pairs of same phase opening portions andreverse phase opening portions, whereby stripping of the light shieldingfilm can be prevented at the part where the pairs are opposed to eachother. In the present embodiment, the same phase opening portions areset in the opening portions on both sides of the pairs opposed to eachother. Referring to FIG. 23 and FIG. 24, same phase opening portion 3 aand same phase opening portion 3 c are set which are opposed to eachother. Therefore, the contact area between transparent substrate 21 andthat part of light shielding film 3 which is sandwiched between samephase opening portion 3 a and same phase opening portion 3 c can beincreased, thereby preventing the stripping of light shielding film 3.

The method of setting a same phase opening portion and a reverse phaseopening portion in the region of the opening portions of theLevenson-type mask may employ, for example, shifter arrangement DA(Design Automation) system. By applying the opening portion settingmethod of the present invention to the shifter arrangement DA, the kindof opening portions of the Levenson-type mask can be set.

FIG. 26 shows an exemplary opening portion setting method in the presentembodiment. A region of opening portions through which light passes isset beforehand for a resist pattern to be formed, and a same phaseopening portion or a reverse phase opening portion is then set in eachregion of opening portions.

First, assuming that a same phase opening portion and a reverse phaseopening portion are paired, a part where the distance between the pairsis shortest is selected. In this part, a same phase opening portion isset in the region of two opening portions opposed to each other, of theregion of four opening portions included in the opposing two pairs.Then, a pair of reverse phase opening portions corresponding to the setsame phase opening portions is set.

Then, it is determined whether or not the distance between the setreverse phase opening portion and another reverse phase opening portionis short so that the stripping of the light shielding film is likely tooccur. If the stripping of the light shielding film is likely to occur,one of the set two same phase opening portions is changed to a reversephase opening portion so that the opening portions in a pair are changedto same phase opening portions. In other words, if the distance betweenthe set reverse phase opening portion and another reverse phase openingportion is too short, the above-noted change is reset and the processproceeds to the next step.

Then, in the region of opening portions where a same phase openingportion and a reverse phase opening portion are not set, the similaroperation is repeated. In this manner, a same phase opening portion anda reverse phase opening portion are set for all the regions of openingportions.

In the example shown in FIG. 26, a same phase opening portion is set inthe order of increasing distance between the pairs. However, the presentinvention is not limited to this manner. Those parts where the distancebetween the pairs is equal to or less than a prescribed value areselected, and among the selected parts, a part where a pattern formed bythe half tone-type mask is present between pairs may be given priorityto set a same phase opening portion.

Furthermore, a shifter may be arranged at the main surface of thetransparent substrate in addition to the concave portion formed in thesurface of the transparent substrate. Therefore, a manufacturing errormay be caused in the formation of the concave portion or the arrangementof the shifter. In other words, a phase difference may be shifted due tothe manufacturing error of the Levenson-type mask. Thus, the patternformed at a part sandwiched between reverse phase opening portions maybe influenced by the shifted phase difference, possibly resulting indeteriorated dimensional accuracy.

However, as in the present embodiment, at least one of the patternsformed by the half tone-type mask is set as a same phase opening portionin the order of increasing distance between the pairs, therebypreventing exposure with a shifted phase resulting from themanufacturing error in manufacturing these masks, and improvingdimensional accuracy.

The other configuration, action, effect, and method are similar to thoseof the first to third embodiments and therefore the description will notbe repeated here.

Fifth Embodiment

Referring to FIG. 27 to FIG. 30, a pattern formation method and a methodof manufacturing a Levenson-type mask in a fifth embodiment of thepresent invention will be described.

FIG. 27 is a schematic plan view of a resist pattern formed by aLevenson-type mask in the present embodiment. Resist patterns 11-13 areformed on a surface of substrate 9. Resist pattern 13 is formed betweenresist pattern 11 and resist pattern 12. First pattern portion 11 a ofresist pattern 11 and first pattern portion 12 a of resist pattern 12are formed by the Levenson-type mask.

Resist pattern 13 includes a first pattern portion 13 a and a secondpattern portion 13 b. In the present embodiment, first pattern portion13 a is formed by the Levenson-type mask. Second pattern portion 13 b isformed by the half tone-type mask.

In the present embodiment, first pattern portions 11 a, 12 a of resistpatterns 11, 12 formed on a conductive film (not shown) such aspolysilicon are used to form the gate electrode of a field effecttransistor, and resist pattern 13 is used to form an interconnection.Active region 50 is formed on opposite sides of first pattern portions11 a, 12 a, where the source region of a field effect transistor and thelike is formed. Resist patterns 11, 12 each are formed in an elementregion 51 in which an element is formed. An element isolation region 52is a region where an element such as a field effect transistor is notformed. Resist pattern 13 is formed in element isolation region 52.

FIG. 28 shows a schematic plan view of the Levenson-type mask in thepresent embodiment. In the Levenson-type mask in the present embodiment,a same phase opening portion 4 a and a reverse phase opening portion 4 bare formed in a light shielding film 4 to form first pattern portion 11a of resist pattern 11. A same phase opening portion 4 c and a reversephase opening portion 4 d are also formed to form a resist pattern 12.

In the present embodiment, the linear first pattern portion 13 b ofresist pattern 13 is also formed by the Levenson-type mask. Here, resistpattern 13 sandwiched between resist pattern 11 and resist pattern 12 isa part that is conventionally formed by the half tone-type mask. In thepresent embodiment, the size of reverse phase opening portion 4 b andsame phase opening portion 4 c arranged at the position where resistpattern 13 is sandwiched therebetween is enlarged. First pattern portion13 a of resist pattern 13 is formed by the light passing through reversephase opening portion 4 b and the light passing through same phaseopening portion 4 c (see FIG. 27).

FIG. 29 shows a schematic plan view of the half tone-type mask in thepresent embodiment. A light shielding portion 7 a is formed at thesurface of transparent substrate 19. Light shielding portion 7 a isformed to cover first pattern portion 11 a of resist pattern 11, firstpattern portion 12 a of resist pattern 12 and first pattern portion 13 aof resist pattern 13 (see FIG. 27). Light shielding portion 7 a isformed corresponding to opening portions 4 a-4 d of the Levenson-typemask (see FIG. 28).

Half tone portions 7 b, 7 c are formed corresponding to second patternportions 11 b, 12 b of resist patterns 11, 12. Half tone portion 7 d isformed corresponding to second pattern portion 13 b of resist pattern 13(see FIG. 27).

Referring to FIG. 27, when the distance between resist pattern 13 formedin element isolation region 52 and the exposure region of theLevenson-type mask falls within a prescribed distance, if the entireresist pattern 13 is formed by exposure using the half tone-type mask,the exposure light passing through reverse phase opening portion 4 b andsame phase opening portion 4 c has the greater effect on first patternportion 13 a of resist pattern 13. As a result, the dimensions of firstpattern portion 13 a of resist pattern 13 may vary widely.

If within the above-noted prescribed distance, the size of the samephase opening portion and the reverse phase opening portion arranged onthe outer side of the interconnection pattern to be formed by the halftone-type mask is enlarged so that the interconnection pattern is formedby the Levenson-type mask.

The method of manufacturing a semiconductor device in the presentembodiment includes the step of forming the second pattern portion bythe Levenson-type mask when the distance between the second pattern tobe formed by the half tone-type mask and the region exposed through theopening portion of the Levenson-type mask is such a distance that has asubstantial effect on the dimensional variations of the second pattern.

In other words, in the present embodiment, even for the pattern otherthan a minute pattern or a pattern requiring dimensional accuracy whichis to be formed by the Levenson-type mask, if the distance from thepattern to be formed by the Levenson-type mask is within a prescribeddistance, that pattern is formed by exposure using the Levenson-typemask.

FIG. 30 and FIG. 31 show schematic plan views illustrating the openingportion setting step of setting an opening portion in the method ofmanufacturing a Levenson-type mask in the present embodiment. In thepresent embodiment, an opening portion of the Levenson-type maskcorresponding to a resist pattern to be formed is set by a calculator.The calculator includes a program for setting an opening portion of theLevenson-type mask.

FIG. 30 is an illustration of a corresponding part in the calculator.Resist pattern corresponding portions 41-43 are set for a maskcorresponding portion 31. Here, resist pattern corresponding portions41, 42 correspond to resist patterns 11, 12 in FIG. 27. Resist patterncorresponding portion 43 corresponds to resist pattern 13 in FIG. 27.

Then, an active region corresponding portion 44 is set around each ofresist pattern corresponding portions 41, 42. Active regioncorresponding portion 44 corresponds to active region 50 in FIG. 27.

Then, a same phase opening portion 31 a and a reverse phase openingportion 31 b are set on opposite sides of resist pattern correspondingportion 41. A same phase opening portion 31 c and a reverse phaseopening portion 31 d are also set on opposite sides of resist patterncorresponding portion 42.

Resist pattern corresponding portion 43 is sandwiched between reversephase opening portion 31 b and same phase opening portion 31 c. Here, itis assumed that at least one of distance L6 between resist patterncorresponding portion 43 and reverse phase opening portion 31 b anddistance L7 between resist pattern corresponding portion 43 and samephase opening portion 31 c is within a prescribed distance. In otherwords, it is assumed that the design value of the distance between apart exposed through an opening portion and a resist pattern is within aprescribed distance. In the present embodiment, 0.3×λ/NA is used as aprescribed distance, where λ is a wavelength of a light source inexposure and NA is numerical aperture. The prescribed distance in thepresent embodiment is a dimension equivalent to a limit of resolution.

When the distance between the resist pattern corresponding portion andthe opening portions arranged at the parts corresponding to the oppositesides of a resist pattern which is conventionally formed by the halftone-type mask is within the prescribed distance as described above, ifthe both of the opening portions on opposite sides of the resist patternare same phase opening portions, one of them may be changed to a reversephase opening portion.

FIG. 31 is an illustration of the step of setting a dummy active regionin a corresponding part in the calculator. In the present embodiment,shifter arrangement DA (Design Automation) system is employed to set asame phase opening portion and a reverse phase opening portion in theregion of opening portions of the Levenson-type mask.

An active region corresponding portion 44 is set corresponding to eachof resist pattern corresponding portions 41, 42. Resist patterncorresponding portion 43 includes a first pattern corresponding portion43 a and second pattern corresponding portions 43 b, 43 c.

If at least one of the aforementioned distances L6 and L7 is within theabove-noted prescribed distance, dummy active region 45 is set in theregion where resist pattern corresponding portion 43 is formed. It isset such that an active region is virtually formed in a layerimmediately below first pattern portion corresponding portion 43 a ofresist pattern corresponding portion 43. For example, dummy activeregion 45 is set as if first pattern portion corresponding portion 43 awas a gate electrode.

By setting dummy active region 45, first pattern corresponding portion43 a is determined to have, for example, a gate electrode formedtherein, and first pattern corresponding portion 43 a is identified as apattern to be formed by the Levenson-type mask. It is determined that inthe Levenson-type mask a same phase opening portion and a reverse phaseopening portion should be set on opposite sides of first patterncorresponding portion 43 a. Reverse phase opening portion 31 b and samephase opening portion 31 c are expanded such that first pattern 13 a isformed by exposure light transmitted through reverse phase openingportion 31 b and same phase opening portion 31 c shown in FIG. 30. TheLevenson-type mask shown in FIG. 28 is formed based on the data of samephase opening portion and reverse phase opening portion.

In the present embodiment, a calculator program is used to set the kindand size of the opening portion of the Levenson-type mask. When thepatterns formed in the element isolation regions include a partsandwiched between patterns formed by the Levenson-type mask and ifwithin the above-noted prescribed distance, a dummy active region is setand the opening portion is expanded. By setting a dummy active region,the expanded same phase opening portion or reverse phase opening portioncan easily be formed.

In the present embodiment, the calculator program determines that thesame phase opening portion and the reverse phase opening portion shouldbe increased in size so that the same phase opening portion and thereverse phase opening portion are expanded. The method of expanding theopening portions is not limited to this manner. The same phase openingportion and the reverse phase opening portion may be expanded bymutually coupling the opening portions in contact with each other wherethe same phase opening portion and the reverse phase opening portion arefirst set on opposite sides of the first pattern corresponding portion.

In the present embodiment, an interconnection pattern formed in theelement isolation region is formed by the Levenson-type mask, therebyimproving the dimensional accuracy of the above-noted interconnectionpattern. In addition, the focus tolerance can be improved and circuitpatterns can be formed at high yields.

In the diagrams of the foregoing embodiments, the same or correspondingparts are denoted with the same reference characters.

In accordance with the present invention, it is possible to provide apattern formation method to allow formation of a minute pattern. It isalso possible to provide a method of manufacturing a Levenson-type maskto allow formation of a minute pattern.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

1. A method of forming a pattern including a first pattern having afirst minimum dimension which is a minimum dimension of spanningdimensions and a second pattern having a second minimum dimension whichis a minimum dimension of spanning dimensions, comprising: a firstexposure step of performing an exposure for forming said first patternusing a Levenson-type mask; and a second exposure step of performing anexposure for forming said second pattern using a half tone-type mask,wherein when said second minimum dimension is at least 1.3 times saidfirst minimum dimension, an exposure amount of said second exposure stepis set to be at most an exposure amount of said first exposure step. 2.The method of forming a pattern according to claim 1, wherein saidsecond exposure step is performed using said half tone-type mask havinga transmittance set such that an exposure amount is smaller than theexposure amount of said first exposure step.
 3. The method of forming apattern according to claim 1, wherein the method is used inmanufacturing a semiconductor device based on a design standard of atmost 65 nm and is performed such that an ILS value obtained by thefollowing equation is at least 34:ILS value=(1/Is)×(ΔI/Δx)  (1) where Is is a slice value for a width of80 nm of a line-shaped pattern, and (ΔI/Δx) is a gradient at a point ofa slice value in a light intensity line.
 4. The method of forming apattern according to claim 1, wherein at least one of said Levenson-typemask and said half tone-type mask is formed to have optical proximitycorrection.
 5. A method of forming a pattern including a first patternhaving a first minimum dimension which is a minimum dimension ofspanning dimensions and a second pattern having a second minimumdimension which is a minimum dimension of spanning dimensions,comprising: a first exposure step of performing an exposure for formingsaid first pattern using a Levenson-type mask; and a second exposurestep of performing an exposure for forming said second pattern using ahalf tone-type mask, wherein when said second minimum dimension is atleast 1.0 time and at most 1.1 times said first minimum dimension, anexposure amount of said second exposure step is set to be greater thanan exposure amount of said first exposure step.
 6. The method of forminga pattern according to claim 5, wherein at least one of saidLevenson-type mask and said half tone-type mask is formed to haveoptical proximity correction.